Broken tool detector

ABSTRACT

Accessory apparatus for a machine tool, to detect breakage of a tool bit and stop the machine, consists of a combined valve body, valve-actuating feeler and antideflection member mounted on the bushing plate of the machine, and a pneumatic system responsive to actuation of the valve by the feeler for stopping the machine and for resetting the feeler.

O United States Patent [151 3,647,998

Rohraff, Sr. 5] Mar. 7, 1972 [54] BROKEN TOOL DETECTOR 3,241,402 3/1966Crowell et al ..408/6 [72] Inventor: Harry E. Rohraff, Sr., 16104Pierson Avenue, Detroit, Mich. 48219 Primary Exammer'pavld pAttorneyHarness, Dickey & Pierce [22] Filed: Sept. 14, 1970 [211 App].No.: 71,757 ABSTRACT Accessory apparatus for a machine tool, to detectbreakage of 52 US. Cl ..200/6l.42 408/6 ZOO/61.18 a and the machine [51]body, valve-actuating feeler and antideflection member 53 Field ofSearch,.408/6;200/61.42, 61.18; mounted on the bushing Plate of the machine,and 8 W 137/ 7 70 matic system responsive to actuation of the valve bythe feeler for stopping the machine and for resetting the feeler. 56 f l1 Re erences Cited 20 Claims, 18 Drawing Figures UNITED STATES PATENTS8/1951 Cardweil ..l37/67 X Patented March 7, 1972 s Sheets-Sheet 1 Am 5.lea/mum; we

INVENTOR.

BY J I QI- 4 I ATTO/P/VV &

Patented March 7, 1972 6 Sheets-Sheet 4.

Patented March 7, 1972 6 Sheets-Shoot 5 n E M /I. w F L b/ .l 1 M f. KWm 1 a y m r W V. r m a W 4 V8 Patented March' 1.972

- 1 6 Shoet-Shoet 6 I ma;

BROKEN TOOL DETECTOR RELATED APPLICATION This application is acontinuation-in-part of my previously filed copending application Ser.No. 284, filed Jan. 2, I970.

BACKGROUND OF THE INVENTION This invention relates to power tools andhas particular application to devices for locating a broken tool, suchas a drill, reamer, punch or the like, used with high-productionmachinery, and for preventing continued operation of the machinery in amanner which might cause damage or the production of imperfect work.

An object of the invention is to provide an improved system and devicearranged to indicate the existence of a broken tool and to automaticallyshut down the machine when such broken tool is detected.

Another object of the invention is to provide an improved system anddevice of the character indicated which is comparatively inexpensive tomanufacture and install, compact, simple and reliable.

Another object of the invention is to provide an improved broken tooldetecting device having a sensing element movable across the path of butnormally blocked by the tool bit, when the tool is in normal workingcondition, but which permits and causes the sensing element to moveacross such path, and shut down the machine when the tool bit is broken.

Another object of the invention is to provide apparatus of the characterindicated which may be used on transfer machines, dial machines,trunnion machines, or any other type of multiple station largeequipment.

Another object of the invention is to provide an improved sensing deviceadapted to be mounted on a guide bushing carrier and which is adapted tocheck the condition of tool bits.

operating on close center distances.

Another object of the invention is to provide an improved broken tooldetector which is formed with limited built in leakage and arranged sothat the operating air pressure may keep the parts of the detectorclean.

Another object of the invention is to provide such an improved mechanismincorporating an antideflection bushing arranged to maintain alignmentof the tool bit while the same is being checked and guided into thedrill bushing.

Other objects and advantages will become apparent upon consideration ofthe present disclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic sideelevational view of a machine equipped with the invention;

FIG. 2 is an enlarged horizontal section taken substantially on line 2-2of FIG. 1;

FIG. 3 is an end view taken on the line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken as indicated by the line and arrows 4-4of FIG. 2 but showing a modified construction;

FIG. 5 is a sectional elevational view taken substantially on the line5-5 of FIG. 4;

FIG. 6 is a view taken substantially on the line 6-6 of FIG.

FIG. 7 is a plan view of a modified sensing unit;

FIG. 8 is a side elevational view thereof;

FIG. 9 is a cross section taken substantially on the line 9-9 of FIG. 7and looking in the direction of the arrows;

FIG. 10 is a schematic diagram of a preferred control system;

FIG. 11 is a somewhat diagrammatic sectional elevational view of amodified stop mechanism;

FIG. 12 is a schematic view similar to FIG 10, showing a modifiedcontrol system adapted for use with the stop mechanism of FIG. 11;

FIGS. 13 and 14 are plan and elevational views, respectively, of amodified sensing and time delay mechanism;

FIGS. 15 and 16 are similar plan and elevational views of anothermodified sensing mechanism;

FIG. 17 is a diagrammatic end view of the same showing positions assumedby a drill bit during resetting of the sensing unit; and

FIG. 18 is a detailed section taken substantially on the line l818 ofFIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED FORMS OF THE INVENTION Referringnow more particularly to the drawing, reference character 7 indicatesthe base of a production machine having ways 12 and a reciprocating head13, on which is mounted a conventional electric motor 14, gear reduction15, tool-holding spindle 16, bushing plate carrier 17, and awork-holding fixture 18 in which is mounted a workpiece 19 which isbeing drilled by the drill bit 20, which rotates with the tool spindle16. In other types of machines the work may rotate while the tool bitremains stationary. The bushing plate carrier 17 has an opening 23therein in which is mounted a tool guide bushing 24 in which the tool 20reciprocates during its normal cycle of operation. The guide bushing 24is held in position by means of a retainer 25 and a machine screw 26.

All of the elements just described constitute conventional parts of awell-known machine and comprise no part of the invention except as theyare combined with elements hereinafter described.

A combined valve housing and feeler support body 21 is secured bymachine screws 22 (FIGS. 2 and 3) to the bushing plate carrier 17. Theassembly 21 is preferably made of two parts, comprising a blocklike body27 and a cover plate 28.

' The body 27 (FIG. 2) is provided with a rectangular valve chamber 29,an extension 30 of which defines an opening and slideway for a feelerarm 33 integral with a valving element 31 slidable in chamber 29. Arm 33is movable radially across the path of the drill 20. The valving elementand feeler arm are biased away from the drill path by spring 32. Nearits free end the feeler arm 33 is provided with a bore 34 through whichthe tool bit 20 slidably extends during normal operation of the machineso that under normal conditions, when the tool bit 20 is unbroken, itsperiphery will hold the feeler and valve element 31 against the pressureof the spring 32.

A pair of ports 35, 36 in opposite sides of body 27 open into chamber 29in positions to be blocked by valve member 31 when the latter is in theposition in which it is held by an unbroken tool bit (spring 32compressed). Port 35 is illustrated as the air inlet port and 36 as anexhaust port open to the atmosphere ('FIG. 3), although theseconnections can be reversed where such is more convenient. A thirdopening 37 communicates with the chamber 29 at the end opposite thefeeler arm 33 and serves as a reset air inlet, the purpose of which willappear hereinafter. The ports 35 and 37 are supplied with air underpressure from a suitable source (not shown).

In normal operating work cycles, the tool bit 20 will reciprocate in theguide bushing 24, and in an antideflection bushing 38 carried by anextension portion 28' of top plate 28. In the normal retracted positionof the tool bit, indicated at X in FIG. 2, only the end of the bitoverlaps the feeler. If breakage of the bit occurs, when the portionattached to the spindle 16 is thereafter withdrawn, on the next cycle,there will be nothing to hold the feeler in its normal position, and thefeeler and valve will be moved away from the tool by spring 32,unblocking ports 35, 36 and venting the main air supply line 35Aconnected to port 35. This will cause a reduction in pressure in the airline 35A, tripping a pressure switch 358 and opening the circuit throughan electric line 35C connected to the control panel of the machine andcausing the machine to stop, or at least stopping the head 13 (dependingupon the details of the preferred machine control setup, which ,ofcourse do not form a part of the present invention).

After the machine stops, the operator may manually control the head 13through the control panel (not shown) in such manner as to cause thehead 13 to bypass the limit switch 41 which limits the normal fullretract position so that the head 13 will move farther back and actuatethe switch 42, which in turn actuates the reset air supply, returns thefeeler to projected position, and reblocks port 35. in this position thehead 13 and the spindle are retracted far enough so the tool may bereplaced. When the tool is replaced, the head is again manually operatedforwardly to bypass the switch 41 and resume its normal position whereinits switch-actuating shoes 40A, 41A are between and controlled by thelimit switches 40 and 41 for automatic cycling.

When the head has moved forwardly far enough so that the cam 40Astrikes, switch 40, the tool bit, if present and unbroken, is in thefeeler opening, and so is in position to restrain movement of thefeeler. The position of switch 40 corresponds to the full-in position ofthe tool bit, and it is so connected as not only to reverse the head butalso to return the circuit of reset air switch 42 to the air offposition and so cut off the reset air supply to port 37. The tool bitthen restrains the feeler and the reset limit switch 42 remains inactiveand the reset air off until the head is again moved all the way to therear after another broken tool is encountered or when it is desired toremove a dull tool.

In FIG. 4 I show a modified form of the device in which the cover plate28A of the housing 21A is secured to the body 27A by means of one longmachine screw 22A, hollow dowel 45, and three short machine screws 228.The long machine screw 22A is threaded into a suitable tapped hole inthe bushing plate carrier 17, so that upon removal of the short machinescrews 22B, the cover 28A may be pivoted around the long machine screw22A, so the broken tool may be removed and replaced with another. Thedevice functions in other respects as herein previously described.

Another modified sensing mechanism, shown in FIGS. 7-9, is similarlyadapted to be attached to the bushing plate of a machine by machinescrews 51, 51 positioned at three of the comers of the rectangular body54 and a spring-pressed latching and locating pin 52 at the fourthcomer, which is one of the corners closest to the bit path. Screws 51,51 extend through and retain the cover plate 55 as well as serving toattach the assembly to the bushing plate. At one of the corners fartherfrom the bit path the screw 51', which is the pivot screw, extendsthrough a hollow dowel 56 which is accurately fitted in the bushingplate and in the bottom of the body 54. In order to move the sensingassembly away from the alignment bushing in the bushing plate, thescrews 51 are removed, pin 52 is lifted, and the assembly is pivotedaround screw 51' and dowel 56.

The cover plate 55 similarly extends outwardly across the path of thetool bit where it carries an antidefiection bushing 58 closely overlyingthe feeler tip 60. In this embodiment the feeler tip 60 is formed as aseparate and renewable element removably secured to the feeler stem 64of the valve element 62. The feeler stem 64 is of reduced diameter andthe valve element 62 is formed as a piston which is movable upwardly, asviewed in FIGS. 7 and 8, by resetting air introduced through one of theopposed side ports 68, 69 or cover port 67, the other two of such portsbeing permanently blocked. A spring 70 behind the valve piston 62 biasesthe feeler tip outwardly against the tool, while resetting air maintainsthe valve piston in the left end position, and the spring compressed, inwhich position the main control air inlet and exhaust ports 71 and 72and cover port 73 are blocked. in this embodiment, in order to providemaximum accessibility for the making of connections, cover plate 55contains an additional port 67 usable in place of the side ports 68, 69,as noted above, and the cover plate is also provided with a port 73usable, in place of one of the ports 71, 72, as a control air or ventport. Thus the specific connections shown and described are variable asmay be convenient or necessary to accommodate other parts.

FIG. shows in diagrammatic form a preferred control system adapted to beused with the sensing mechanism of FlGS. 7-9. A source of air underpressure delivered by a conduit 75 through suitable filtering anregulating means 76 and 77 is connected through an adjustable pressureregulator 78 and via conduits 79, 80 to a pressure switch 82 which bysuch pressure is normally held closed to maintain operation of themachine in the normal manner under the control of the electrical mastercontrol panel 84. A pressure gauge 81 is preferably provided in the line79 beyond the regulator 78. Line 80 is also connected to the side port72 of the sensing unit.

The main air supply upstream of the regulator 78 is also connected by aconduit 85 to an air limit valve 86 and a time delay valve 88. The timedelay valve is in series with the reset air port 69 of the sensing unit,to which it is connected by a conduit 89. Conduit 85 is connected to aside inlet port 90 of the time delay valve, which port is during normaloperation of the machine maintained in communication with conduit 89 andreset air port 69 by the valve 88.

The machine is equipped with a cam 92 for actuating the air limit valve86 at the same time the rear reversing switch corresponding to theswitch 41 of the first embodiment is actuated. At other times the valve86 is held closed by its biasing spring, and the biasing spring of timedelay valve 88 therefore maintains the latter valve in theaforementioned position to constantly supply air to the reset port 69and maintain the sensing tip 60 slightly spaced from the tool bit.

At each retraction of the slide in normal operation of the machine, thecam 92 opens the normally closed valve 86, which then supplies airthrough branch lines 94, 95 to one end of the valve spool of valve 88.Valve 88 is thereby immediately shifted to closed position, by airpressure delivered to its right end, as the parts are shown in FIG; 10,interrupting the supply to the reset port 69 and permitting the feelertip to move into engagement with the tool bit under the influence of thebiasing spring 70. Assuming the tool to be unbroken, the feeler tip, byengagement with the tool bit, arrests movement of the valve piston 62before the latter is moved far enough to unblock the air inlet port 72,and the machine accordingly continues operation, the head reversing andmoving forwardly in the normal manner. At the same time that air isdelivered to the right end of the time delay valve via line 95, it isdelivered to the left end of the valve through an adjustable orifice 99and a conduit 100. By virtue of the presence of the orifice 99, however, the pressure via line 100 is not sufficient, for a predeterminedinterval, to prevent closing of the valve 88. However, the pressure vialine 100 is augmented by the biasing spring 87 so that when the pressurebuilds up to an equalized condition, valve 88 reopens the supply to thereset port under the influence of its biasing spring. This setting ispreferably such that the time interval is short and merely of sufficientlength to check the tool bit.

As previously explained, the normal travel of the tool bit with relationto the work is such that, at full retraction, the tip of the tool bitremains in overlapping relation with respect to the tip of the feeler.if the tool has broken so that such overlapping relation does not exist,when the reset air to port 69 is interrupted as described above, thefeeler moves across the path of the tool bit far enough to permit thevalve piston 62 to unblock ports 71 and 72. The air pressure in line 80thereupon drops, and the pressure switch 82, being biased to theposition to interrupt the circuit to the machine, is actuated to stopthe machine. Thereafter the head may be moved back and the tool replacedas described above in connection with the first embodiment.

It will be understood that the air pressure delivered via line 85 andthe time delay valve to the reset port will be substantially higher thanthe pressure delivered through regulator 77 to the control line 80leading to the pressure switch and to the main air inlet port 72 of thesensing unit. The regulated air pressure in the control line maynevertheless be substantial (e.g.: 25-90 p.s.i.) so that the pressuredrop when line 80 is vented through the sensing unit will be substantialand actuation of the pressure switch 82 correspondingly positive. Due tothe quick dumping of the reset air, the feeler spring may be relativelylight, but the actuation of the feeler is rapid. if the pressuredifferential between the supply and the control line 80 established bythe regulator 77 is sufficient the adjustable orifice 78 may be entirelyomitted.

The clearances between the sensing valve and its valve chamber, andbetween the feeler stem and the passage in which it slides, are greatenough to allow a continuous limited escape of air which tendsconstantly to clean the parts and prevent fouling and sticking under theeffects of the cutting oil and chips which are normally present in theenvironment in which these parts operate.

In FIGS. 11 and 12 a modified arrangement is shown for arrestingoperation of the machine in event of tool breakage. In place of thespecial pressure switch 82 which must of course be connected into thecontrol circuit in the master control panel of the machine, means areprovided for stopping the machine by automatically depressing theregular stop button 105 with which the control panel 84A isconventionally equipped. A servo-cylinder 106 is provided with a plunger108 adapted to engage and depress the stop button when actuated by thepiston 110 of the servo-cylinder. The cylinder is suitably mounted overthe button as by bracket 112, and its piston is biased to the stopposition by a spring 114 but normally held off by the main air supplywhich acts upon the opposite side of the piston, to which it isdelivered by a branch line 115 connected to the air supply conduit 80A,and which corresponds to the line 80 shown in FIG. 10. Other parts ofthis embodiment corresponding to parts of the embodiment last describedare designated by like reference characters distinguished by the letterA and will not require detailed redescription. It will be seen that inevent of tool breakage and the consequent venting of the pressure inlines 80A and 115 through the sensing unit, the fall of pressure on theleft side of the piston 110 permits the spring 114 to stop the machineby depressing the button 105.

FIGS. 13 and 14 show a further modified sensing unit incorporating timedelay means and which eliminates the air limit valve 86, the time delayvalve 88 and also the reset air port. The feeler mechanism itself andthe means for actuating the same are basically similar to thearrangement shown in FIGS. 7-9 and corresponding parts are designated bylike reference characters distinguished by the letter B," but the mainair supply, which is delivered to a side port 728 of the sensing unitalso acts as the reset air supply. A spring-pressed plunger 120 attachedto the head of the machine is adapted to engage the end of the spoolvalve 121 which projects from the sensing unit, such engagementoccurring each time the tool and head commence to move inwardly duringnormal operation. During the first portion of such normal forwardmovement the plunger 120 moves the valve 121 through its full stroke,which is relatively short, and the plunger is thereafter restrained bythe bottoming of the valve as the head and tool bit continue theirforward movement. The reset air is conducted from the inlet port 723through a branch passage 125 to a side port 126 in the valve chamberbore 130. The valve 121 is biased outwardly by a compression spring 128beneath its inner end. When the valve is fully projected (head and toolbit retracted) a cross-connecting passage 131 in the valve is alignedwith port 126 and with an opposite port 132 which communicates via abranch passage 133 with the space below a valve spool 628 on the innerend of the feeler stern 648. Thus the reset air is normally effective tomaintain the feeler tip retracted except when the valve 121 is movedinwardly by the plunger 120. The valve 121 also contains a secondcross-connecting passage 134 so spaced from the passage 131 that whenthe valve is fully depressed, the passage 134 reestablishescommunication between passages 125 and 133 to permit resumed conductionof reset air. Thus the delivery of reset air is only interrupted duringthe interval required for the valve 121 to" move between its projectedand fully depressed positions, and such interruption occurs in a shortinterval at the commencement and at the conclusion of each normaloperative stroke of the head and tool bit. The rate of travel of thevalve 121 is variable by an adjustable needle valve 122 which imparts acontrollable dashpot effect to the chamber space beneath valve 121.

At the time of interruption of reset air only the tip of the tool bitoverlaps the feeler, as shown in FIG. 14. Accordingly, if the tool isbroken so that the tip is not present, the feeler will move fartherdown. The stem 64B also acts as a valve which normally blockscommunication between inlet port 728 and a vent port 718 in the oppositeside of the body. A cross-communication passage 137 in stem 64B is sopositioned that if the feeler moves all the way down during theinterruption interval, due to the absence of the blocking effect of thetool bit, passage 137 registers with ports 72B-71B, vents the main airsupply line connected to port 728 and stops the machine in the mannerpreviously described.

FIGS. 15-17 disclose another modified sensing mechanism wherein thefeeler tip 60C is attached to an ejectable feeler stem portion 64C whichalso acts as a piston and as a blocking valve for the main air lineconnected to the side port 72C. The portion 64C is of circular crosssection and together with the feeler tip 60C is also rotatable about itslongitudinal axis in the body 54C. The feeler is normally urged againstthe side of the tool bit by a compression spring 70C behind the stem64C. When a tool bit breaks, the tip and stem are ejected completelyfrom the body, and the main controlling air line connected to port 72Cis thereby vented through the open outer end of the cylindrical bore 141in which the stem is slidable, the machine thereby being stopped eitherby pressure switch mechanism such as is shown in FIG. 10 or by stopbutton operating means such as disclosed in FIG. 11. The control airaids projection of the plunger after its full diameter stem portionmoves out far enough to establish communication between port 72 and thespace behind the stern of the plug. A loose chain 144 may connect thesensing tip and stem assembly to the body to prevent loss, as in theconstruction shown, or these assemblies may be treated as expendable,and a new one substituted whenever a tool breaks.

In view of the fact that air is being supplied to the sensing unit atthe time the operator reinstalls the feeler assembly after a toolbreakage, the wall of the stem 64C is provided with an L-shaped slot145. Pin 148 which also anchors the chain 144 extends into the slot 145.Slot-145 has a straight longitudinal portion extending to the free endof the stem and a short peripheral leg at a position corresponding tofull insertion of the feeler assembly. The straight portion of slot 145is so located that when such part of the slot overengages the pin 148the feeler tip is perpendicular to the path of the tool bit 20C asrequired in the normal operative position shown in full lines in FIG.17, while when the feeler assembly has been fully inserted and turned tothe maximum angle permitted to the peripheral leg of the slot, thefeeler tip assumes the angular position shown in broken lines in FIG. 17wherein it is tipped approximately 45. After a tool breakage, the feelerassembly is inserted and turned to such angular position, so that theperipheral leg of the slot overengages pin 148 to prevent the feelerassembly from being immediately blown out of the sensing unit by thecontrol air. When the tool advances on the first operative stroke, itstrikes the tilted feeler tip, as shown in FIG. 17 straightens it to thetransverse operative full line position and thereafter overlaps the tipto restrain it, so that although the restraining effect of the bitprevents the feeler from being ejected until a tool breakage occurs, thestraight section of the slot is aligned with the pin and permits suchejection in event of breakage of the bit.

Where multiple drills (or other tool bits) are grouped to move to andfrom the work simultaneously, a single time delay valve may serve thesensors for all of such bits. In the case of the embodiment of FIGS. 13and 14, therefore, only a single plunger and valve 121 will be requiredfor each head. Of course, the same principles apply whether the toolsmove with relation to the work or vice versa.

This Detailed Description of Preferred Forms of the Invention," and theaccompanying drawings, have been furnished in compliance with thestatutory requirement to set forth the best mode contemplated by theinventor of carrying out the invention. The prior portions consisting ofthe Abstract of the Disclosure and the Background of the Invention arefurnished without prejudice to comply with administrative requirementsof the (1.5. Pat. Office.

What is claimed is:

1. Means for detecting breakage of a tool bit or the like in a machinetool of the type wherein a bit and workpiece are movable relatively toeach other, comprising a body adapted to be attached to a bushing plateof such a machine, a valving member in the body, a feeler movablysupported by the body and operatively connectable to the valve toactuate the latter, fluid-operable means controllable by the valve forpreventing unwanted relative movement of the workpiece and bit inresponse to breakage of the bit, and means for biasing said feelertoward a portion of the bit, whereby in event said portion of the bit isabsent due to breakage, said feeler and valve are movable to a detectingposition not otherwise attainable.

2. Means as defined in claim 1 wherein said body is of blocklike formhaving a bottom face adapted to bear against the bushing plate of amachine in a position adjacent a bushing through which a tool bitextends during operation of the machine, the feeler projecting from thebody in a position spaced outwardly from said bottom face to overlie thebushing, and an antideflection bushing carried by the body and alsooverlaying the aforementioned bushing at a position spaced farther fromsaid bottom face than, but relatively close to, the

feeler.

3. Means as defined in claim 2 wherein the valving member is movable ina cavity in the body, and a closure plate for the cavity defining theouter face of the body and extending laterally therefrom and carryingsaid antideflection bushing, the feeler being movable in the spacebeneath the laterally extending portion of the closure plate.

4. Means as defined in claim 2 wherein the valving member is movable ina cavity in the body, and a closure plate for the cavity defining theouter face of the body and extending laterally therefrom and carryingsaid antideflection bushing, the feeler comprising an extensionconnected to the valve and slidably extending from the body into, andmovable in, the space beneath the laterally extending portion of theclosure plate. 1

5. In combination with means as defined in claim 1, means for attachingsaid body to a bushing plate in a position such that the feeler mayoverhang a bushing in the plate, said means including a fulcrum screwextending through the body at a position spaced from the bushing andabout which the body may be pivoted to displace the feeler from theoverhanging position.

6. Means as defined in claim 1 wherein said valve is a vent valve biasedto venting position, the feeler having a sensing portion movable towardthe tool bit as the valve commences movement from closed position towardventing position, the feeler and valve being normally blocked frommovement to venting position by the tool bit, whereby a pressure changeinduced by venting may be utilized to arrest an operation of the machinein event breakage of the tool bit permits the feeler and valve to moveto venting position under the influence of the biasing means.

7. In combination with means as defined in claim 6, a servomotor forreturning said valve and feeler from venting position to closedposition.

8. Means as defined in claim 7 wherein said servomotor is operable byair pressure in a direction counter to said bias and to move the valveand feeler to a closed position of the valve wherein said feeler issomewhat spaced from the path of the tool bit.

9. Means as defined in claim 7 wherein said servomotor is operable byair pressure in a direction counter to said bias and to move the valveand feeler to a closed position of the valve wherein said feeler issomewhat spaced from the path of the tool bit, means normallymaintaining counterbiasing pressure in said servomotor, and meansincluding a timer and a valve operable in response to movement of thetool bit carrying portion of the machine to a predetermined position forinterrupting delivery of air pressure to said servomotor during a timedinterval, whereby the biasing means may move the feeler against, or intothe path of, the tool bit, whereby if the bit is not present the feelerand valve move to the venting position.

10. In, a broken tool detecting apparatus adapted for use with a machinetool having a work-supporting portion and a tool bit supporting portion,one of which portions is movable in a predetermined path toward and fromthe other to the extent of a normal travel during operation of themachine, the novelty which comprises, in combination, a vent valvebiased to venting position, means for holding the valve closed againstthe effect of the bias including a feeler operatively connected to thevalve and engageable with the tool bit in a direction lateral to saidpath when said portions are near the fully withdrawn part of said normaltravel, fluid pressure responsive control means for the machine, saidcontrol means being biased to a position to arrest relative movement ofsaid portions of the machine and counterbiasable by fluid pressure, andfluid conducting means connected to said control means and to said ventvalve and adapted to be connected to a source of fluid pressure, wherebysuch relative movement will be arrested by the control means if the ventvalve opens to the venting position due to failure of engagement betweenthe feeler and tool bit.

11. In a broken tool detecting apparatus adapted for use with a machinetool having a work supporting portion and a tool bit supporting portion,one of which portions is movable in a predetermined path toward and fromthe other to the extent of a normal travel during operation of themachine, the novelty which comprises, in combination, a valve biased toone position, counterbiasing means for holding the valve in anotherposition comprising a feeler operatively connected to the valve andbiased to engage the tool bit in a direction lateral to said path whenthe tool bit supporting portion is near the fully withdrawn part of saidnormal travel, fluid pressure responsive control means actuatable toarrest relative movement of said portions of the machine, and meansconnecting said valve to said control means to actuate the latter inresponse to movement of the valve when the feeler moves beyond itsposition of engagement with the tool bit due to failure or absence ofthe tool bit.

12. Apparatus as defined in claim 11 wherein said feeler is biasedtoward the tool bit throughout said normal travel, a secondcounterbiasing means operable by fluid pressure for moving the feeleraway from the tool bit, and means responsive to movement of saidportions to said withdrawn part of the normal travel for disabling saidsecond counterbiasing means.

13. Apparatus as defined in claim 10 wherein said feeler and valve areconnected for simultaneous movement and the biasing means for the valvebiases the feeler toward the tool bit.

14. Apparatus as defined in claim 10 wherein said feeler and valve areconnected for simultaneous movement and the biasing means for the valvebiases the feeler toward the tool bit, counterbiasing means for movingthe feeler away from the tool bit and the valve away from ventingposition, and means responsive to movement of said portion to saidwithdrawn part of the normal travel for disabling said counterbiasingmeans,

15. Apparatus as defined in claim 10 wherein said feeler and valve areconnected for simultaneous movement and the biasing means for the valvebiases the feeler toward the tool bit, fluid-actuatable counterbiasingmeans for moving the feeler away from the tool bit and the valve awayfrom venting position, and means including a timing valve responsive tomovement of said portion to said withdrawn part of the normal travel fordisabling said counterbiasing means.

16. Apparatus as defined in claim 11 wherein said feeler and valve aremovable as a unit and throughout said entire normal travel the biasingmeans urges the feeler toward the tool bit and the valve toward theposition which actuates the control means.

17. Apparatus as defined in claim 16 wherein the valve is a vent valveand the biasing means urges the same to venting position.

18. Apparatus as defined in claim 17 wherein the vent .valve includes abody having an open ended bore and a valving element slidable androtatable in the bore and ejectable therefrom in the venting position,the feeler being rigidly attached to the valving element to rotatetherewith and having a bit-engaging tip rockable into and out of axialalignment with the tool bit with such rotation and contoured to berocked into axial alignment by the tool bit, and keying portions carriedby the body and valving element for holding the valving element againstejection when it is in the bore and is turned to nonaxially alignedposition.

19. In combination with apparatus as defined in claim 11, a secondcounterbiasing means operable by fluid pressure and acting on the valveand feeler to urge the feeler away from the bit and the valve away fromsaid first-mentioned position, and

a second valve actuatable by said relatively movable portions of themachine to interrupt the supply of fluid pressure to said secondcounterbiasing means during movement of said portions in a part of saidnormal travel.

20. Apparatus as defined in claim 19 including a valve body adapted tobe attached to the machine appurtenant to the path of travel of the toolbit, a valving element of said first-mentioned valve being movable insaid body and the feeler being attached to said valving element, saidsecond counterbiasing means including a piston portion of said valvingelement, and means for delivering fluid pressure to said piston portionincluding said second valve, said second valve being movable in thebody.

1. Means for detecting breakage of a tool bit or the like in a machinetool of the type wherein a bit and workpiece are movable relatively toeach other, comprising a body adapted to be attached to a bushing plateof such a machine, a valving member in the body, a feeler movablysupported by the body and operatively connectable to the valve toactuate the latter, fluid-operable means controllable by the valve forpreventing unwanted relative movement of the workpiece and bit inresponse to breakage of the bit, and means for biasing said feelertoward a portion of the bit, whereby in event said portion of the bit isabsent due to breakage, said feeler and valve are movable to a detectingposition not otherwise attainable.
 2. Means as defined in claim 1wherein said body is of blocklike form having a bottom face adapted tobear against the bushing plate of a machine in a position adjacent abushing through which a tool bit extends during operation of themachine, the feeler projecting from the body in a position spacedoutwardly from said bottom face to overlie the bushing, and anantideflection bushing carried by the body and also overlaying theaforementioned bushing at a position spaced farther from said bottomface than, but relatively close to, the feeler.
 3. Means as defined inclaim 2 wherein the valving member is movable in a cavity in the body,and a closure plate for the cavity defining the outer face of the bodyand extending laterally therefrom and carrying said antideflectionbushing, the feeler being movable in the space beneath the laterallyextending portion of the closure plate.
 4. Means as defined in claim 2wherein the valving member is movable in a cAvity in the body, and aclosure plate for the cavity defining the outer face of the body andextending laterally therefrom and carrying said antideflection bushing,the feeler comprising an extension connected to the valve and slidablyextending from the body into, and movable in, the space beneath thelaterally extending portion of the closure plate.
 5. In combination withmeans as defined in claim 1, means for attaching said body to a bushingplate in a position such that the feeler may overhang a bushing in theplate, said means including a fulcrum screw extending through the bodyat a position spaced from the bushing and about which the body may bepivoted to displace the feeler from the overhanging position.
 6. Meansas defined in claim 1 wherein said valve is a vent valve biased toventing position, the feeler having a sensing portion movable toward thetool bit as the valve commences movement from closed position towardventing position, the feeler and valve being normally blocked frommovement to venting position by the tool bit, whereby a pressure changeinduced by venting may be utilized to arrest an operation of the machinein event breakage of the tool bit permits the feeler and valve to moveto venting position under the influence of the biasing means.
 7. Incombination with means as defined in claim 6, a servomotor for returningsaid valve and feeler from venting position to closed position.
 8. Meansas defined in claim 7 wherein said servomotor is operable by airpressure in a direction counter to said bias and to move the valve andfeeler to a closed position of the valve wherein said feeler is somewhatspaced from the path of the tool bit.
 9. Means as defined in claim 7wherein said servomotor is operable by air pressure in a directioncounter to said bias and to move the valve and feeler to a closedposition of the valve wherein said feeler is somewhat spaced from thepath of the tool bit, means normally maintaining counterbiasing pressurein said servomotor, and means including a timer and a valve operable inresponse to movement of the tool bit carrying portion of the machine toa predetermined position for interrupting delivery of air pressure tosaid servomotor during a timed interval, whereby the biasing means maymove the feeler against, or into the path of, the tool bit, whereby ifthe bit is not present the feeler and valve move to the ventingposition.
 10. In a broken tool detecting apparatus adapted for use witha machine tool having a work-supporting portion and a tool bitsupporting portion, one of which portions is movable in a predeterminedpath toward and from the other to the extent of a normal travel duringoperation of the machine, the novelty which comprises, in combination, avent valve biased to venting position, means for holding the valveclosed against the effect of the bias including a feeler operativelyconnected to the valve and engageable with the tool bit in a directionlateral to said path when said portions are near the fully withdrawnpart of said normal travel, fluid pressure responsive control means forthe machine, said control means being biased to a position to arrestrelative movement of said portions of the machine and counterbiasable byfluid pressure, and fluid conducting means connected to said controlmeans and to said vent valve and adapted to be connected to a source offluid pressure, whereby such relative movement will be arrested by thecontrol means if the vent valve opens to the venting position due tofailure of engagement between the feeler and tool bit.
 11. In a brokentool detecting apparatus adapted for use with a machine tool having awork supporting portion and a tool bit supporting portion, one of whichportions is movable in a predetermined path toward and from the other tothe extent of a normal travel during operation of the machine, thenovelty which comprises, in combination, a valve biased to one position,counterbiasing means for holding the valve in another positiOncomprising a feeler operatively connected to the valve and biased toengage the tool bit in a direction lateral to said path when the toolbit supporting portion is near the fully withdrawn part of said normaltravel, fluid pressure responsive control means actuatable to arrestrelative movement of said portions of the machine, and means connectingsaid valve to said control means to actuate the latter in response tomovement of the valve when the feeler moves beyond its position ofengagement with the tool bit due to failure or absence of the tool bit.12. Apparatus as defined in claim 11 wherein said feeler is biasedtoward the tool bit throughout said normal travel, a secondcounterbiasing means operable by fluid pressure for moving the feeleraway from the tool bit, and means responsive to movement of saidportions to said withdrawn part of the normal travel for disabling saidsecond counterbiasing means.
 13. Apparatus as defined in claim 10wherein said feeler and valve are connected for simultaneous movementand the biasing means for the valve biases the feeler toward the toolbit.
 14. Apparatus as defined in claim 10 wherein said feeler and valveare connected for simultaneous movement and the biasing means for thevalve biases the feeler toward the tool bit, counterbiasing means formoving the feeler away from the tool bit and the valve away from ventingposition, and means responsive to movement of said portion to saidwithdrawn part of the normal travel for disabling said counterbiasingmeans.
 15. Apparatus as defined in claim 10 wherein said feeler andvalve are connected for simultaneous movement and the biasing means forthe valve biases the feeler toward the tool bit, fluid-actuatablecounterbiasing means for moving the feeler away from the tool bit andthe valve away from venting position, and means including a timing valveresponsive to movement of said portion to said withdrawn part of thenormal travel for disabling said counterbiasing means.
 16. Apparatus asdefined in claim 11 wherein said feeler and valve are movable as a unitand throughout said entire normal travel the biasing means urges thefeeler toward the tool bit and the valve toward the position whichactuates the control means.
 17. Apparatus as defined in claim 16 whereinthe valve is a vent valve and the biasing means urges the same toventing position.
 18. Apparatus as defined in claim 17 wherein the ventvalve includes a body having an open ended bore and a valving elementslidable and rotatable in the bore and ejectable therefrom in theventing position, the feeler being rigidly attached to the valvingelement to rotate therewith and having a bit-engaging tip rockable intoand out of axial alignment with the tool bit with such rotation andcontoured to be rocked into axial alignment by the tool bit, and keyingportions carried by the body and valving element for holding the valvingelement against ejection when it is in the bore and is turned tononaxially aligned position.
 19. In combination with apparatus asdefined in claim 11, a second counterbiasing means operable by fluidpressure and acting on the valve and feeler to urge the feeler away fromthe bit and the valve away from said first-mentioned position, and asecond valve actuatable by said relatively movable portions of themachine to interrupt the supply of fluid pressure to said secondcounterbiasing means during movement of said portions in a part of saidnormal travel.
 20. Apparatus as defined in claim 19 including a valvebody adapted to be attached to the machine appurtenant to the path oftravel of the tool bit, a valving element of said first-mentioned valvebeing movable in said body and the feeler being attached to said valvingelement, said second counterbiasing means including a piston portion ofsaid valving element, and means for delivering fluid pressure to saidpiston portion including said second valve, said second valve beingmovable in the body.